Polycrystalline silicon column and polycrystalline silicon wafer

ABSTRACT

A polycrystalline silicon wafer is provided. The polycrystalline silicon wafer, includes a plurality of silicon grains, wherein the carbon content of the polycrystalline silicon wafer is greater than 4 ppma, and the resistivity of the polycrystalline silicon wafer is greater than or equal to 1.55 Ω-cm.

BACKGROUND

The disclosure relates to a polycrystalline silicon column and apolycrystalline silicon wafer.

A solar cell is a photoelectric device which generates electric energyby absorbing sunlight and performing photovoltaic conversion by means ofa photovoltaic effect. Currently, solar cell materials are mainlysilicon materials, as silicon is the second most accessible element onearth and has advantages of having low material cost, is nontoxic, has ahigh stability and the like, and the application of silicon in thesemiconductor field has had a profound foundation.

Solar cells mainly made from silicon material are divided into threetypes, i.e., monocrystalline silicon, polycrystalline silicon andamorphous silicon. Using polycrystalline silicon as the raw material ofa solar cell is mainly based on the consideration of cost. As comparedwith monocrystalline silicon manufactured by the existing Czochralskimethod (CZ method) and floating zone method (FZ method), the cost of thepolycrystalline silicon is much cheaper relatively.

The polycrystalline silicon used for manufacturing solar cells isconventionally produced by using a general casting process. In brief,the silicon with a high purity is melted in a mold (e.g., a quartzcrucible), and then is cooled under controlled solidification to form apolycrystalline silicon ingot. Then, the polycrystalline silicon ingotis generally cut into square wafers, which will be assembled into a cellby a solar cell manufacturer.

The Journal of Crystal Growth, 312, 2010, p. 1572-1576 published amethod for growing high-purity polycrystalline silicon of solar cell byusing a directional solidification crystal-growing furnace. As disclosedin the conventional method as described above, and generallyconventionally understood, in the crystal-growing process volatilecarbon monoxide gas can be easily generated and, if the content of thecarbon monoxide incorporated into a silicon melt is too high, the carbonand oxygen will segregate and separately precipitate or otherwise beincorporated into the solidified crystal formed from the melt. Theoxygen-containing sites of a solidified ingot are known to behave asgettering sites for impurities and the influence the mechanical strengthof a wafer formed therefrom, which can increase the effect of othercrystal defects on degrading the crystal quality. Furthermore, thecarbon incorporated in the conventional method as described above caneasily generate a silicon carbide precipitate through the reactionbetween the carbon and silicon in the melt, which may reduce the shuntresistance (R shunt) of a cell, thereby causing more electric leakagephenomenon. Therefore, it is believed by those of ordinary skills in theart that, the too-high carbon and oxygen content causes theaforementioned instance, and thus the photovoltaic conversion efficiencyis degraded.

The aforementioned description is only used for providing the backgroundtechnology, rather than admitting that the aforementioned descriptiondiscloses the subject matter of the disclosure. The aforementioneddescription does not constitute the prior art of the disclosure, and anyof the aforementioned description should not be considered as any partof the disclosure.

SUMMARY

An embodiment of the disclosure provides a polycrystalline siliconcolumn having a crystal-growing direction. The aforementionedpolycrystalline silicon column includes a plurality of silicon grainsgrowing along a crystal-growing direction, wherein in thecrystal-growing direction, the average grain size of the silicon grainsand the resistivity of the polycrystalline silicon column have oppositevariation in their trends.

Another embodiment of the disclosure provides a polycrystalline siliconcolumn having a crystal-growing direction. The aforementionedpolycrystalline silicon column includes a plurality of silicon grainsgrowing along a crystal-growing direction, wherein in thecrystal-growing direction, the average grain size of the silicon grainsand the oxygen content of the polycrystalline silicon column haveopposite variation in their trends.

A further embodiment of the disclosure provides a polycrystallinesilicon column having a crystal-growing direction. The aforementionedpolycrystalline silicon column includes a plurality of silicon grainsgrowing along a crystal-growing direction, wherein in thecrystal-growing direction, the average grain size of the silicon grainsand the defect area ratio of the polycrystalline silicon column have thesame variation in their trends, and the overall average defect arearatio of the polycrystalline silicon column is less than or equal to2.5%.

Another embodiment of the disclosure provides a polycrystalline siliconwafer including a plurality of silicon grains, wherein thepolycrystalline silicon wafer has a carbon content greater than 4 partsper million atoms (ppma), and a resistivity greater than or equal to1.55 Ω-cm.

A further embodiment of the disclosure provides a polycrystallinesilicon wafer including a plurality of silicon grains, wherein thepolycrystalline silicon wafer has a carbon content greater than 4 ppma,and an oxygen content greater than or equal to 5.5 ppma.

Yet a further embodiment of the disclosure provides a polycrystallinesilicon wafer including a plurality of silicon grains, wherein thepolycrystalline silicon wafer has a carbon content greater than 4 ppma,and an average defect area ratio less than or equal to 1.5%.

The polycrystalline silicon column of the disclosure has a higher carboncontent, and especially the bottom section thereof has a higher carboncontent and a lower defect area ratio, such that the polycrystallinesilicon wafer manufactured by cutting the polycrystalline silicon columnalso has a higher carbon content and a lower defect area ratio, andtherefore a higher photovoltaic conversion efficiency.

The technical features and advantages of the disclosure summarizedrelatively widely above make the detailed description of the disclosurehereafter better understood. Other technical features and advantagesconstituting the subject matter of the claims of the disclosure will bedescribed hereafter. It should be understood by those of ordinary skillsin the art of the disclosure that, the object of the disclosure can beachieved by modifying or designing other structures or processes. Itshould also be understood by those of ordinary skills in the art of thedisclosure that, such an equivalent construction cannot depart from thespirit and scope of the disclosure as defined by the accompanyingclaims.

BRIEF DESCRIPTION OF DRAWINGS

Aspects of the disclosure will be understood best by reading thefollowing detailed description in connection with the drawings. Itshould be noted that, according to the standard implementation of theindustry, various features are not drawn to scale. In practical, forclarity of discussion, dimensions of various features may be arbitrarilyincreased or decreased.

FIG. 1 illustrates a DSS (directional solidification system)crystal-growing furnace used by an embodiment of the disclosure;

FIG. 2 illustrates a method for manufacturing a polycrystalline siliconingot according to an embodiment of the disclosure;

FIG. 3 illustrates a method for manufacturing a polycrystalline siliconingot according to a control group of the disclosure;

FIG. 4 illustrates a relationship curve of the minority carrier lifetimeof the polycrystalline silicon column according to an embodiment of thedisclosure versus the crystal-growing direction;

FIG. 5 is a relationship graph of the polycrystalline silicon columnaccording to an embodiment of the disclosure, between the carbon contentin the crystal-growing direction and the height ratio of the availablesection of the polycrystalline silicon column;

FIG. 6 is a relationship graph of the polycrystalline silicon columnaccording to a control example, between the carbon content in thecrystal-growing direction and the height ratio of the available sectionof the polycrystalline silicon column;

FIG. 7 is a distribution diagram of the carbon content in the bottomsection of the polycrystalline silicon column according to an embodimentof the disclosure;

FIG. 8 is a distribution diagram of the carbon content in the bottomsection of the polycrystalline silicon column according to a controlexample;

FIG. 9 illustrates a schematic diagram of locations for measuring thecarbon content of the polycrystalline silicon column of the embodiment;

FIG. 10 is a relationship graph between the average grain sizes of thesilicon grains of the polycrystalline silicon columns according to anembodiment of the disclosure and according to a control example and theavailable-section height ratios of the polycrystalline silicon columns;

FIG. 11 is a distribution diagram of the polycrystalline silicon ingotaccording to an embodiment of the disclosure versus the ratio of anaverage grain size in the crystal-growing direction to the radial lengthof the crystalline ingot;

FIG. 12 is a distribution diagram of the polycrystalline silicon ingotaccording to a control example versus the ratio of an average grain sizein the crystal-growing direction to the radial length of the crystallineingot;

FIG. 13 is a distribution diagram of a polycrystalline brick accordingto an embodiment of the disclosure versus the ratio of the grain size inthe crystal-growing direction to the radial length of the crystallineingot;

FIG. 14 is a relationship diagram between the resistivity of thepolycrystalline silicon column according to an embodiment of thedisclosure and the height ratio of the available section of thepolycrystalline silicon column;

FIG. 15 is a relationship diagram between the oxygen content of thepolycrystalline silicon column according to an embodiment of thedisclosure and the height ratio of the available section of thepolycrystalline silicon column; and

FIG. 16 is a relationship diagram between the defect area ratio of thepolycrystalline silicon column according to an embodiment of thedisclosure and the height ratio of the available section of thepolycrystalline silicon column.

DETAILED DESCRIPTION

The following disclosure provides many different embodiments andexamples to implement different features of the application. Theparticular examples of elements and configurations are describedhereafter so as to simplify the disclosure of the application. Ofcourse, these are only used as examples, rather than limiting theapplication. For example, in the following description, forming a firstfeature on or above a second feature includes forming the first featureas being directly in contact with the second feature, and also includesthe embodiment of forming other features between the first feature andthe second feature, such that the first feature and the second featureare not directly in contact with each other. Furthermore, the numericalsymbols and/or characters are repeatedly used in different examples ofthe application. Such a repeat is used for the purpose of simplifyingand clarifying, rather than controlling the relationship betweendifferent embodiments and/or the discussed architecture.

Moreover, the application can use simplified illustration of spatialcorresponding phrases, such as “under”, “below”, “higher than”,“relatively higher” and the like to describe the relationship between anelement or feature and another element or feature in the drawings. Thespatial corresponding phrases are used as including differentorientations of a device during the use or operation, in addition toincluding the orientations described in the drawings. The device may belocated (rotated by 90 degrees or in other orientations), and thespatial corresponding descriptions used in the application can beexplained accordingly.

The embodiments of the disclosure disclose several techniques forimproving a carbon content of a polycrystalline silicon column or apolycrystalline silicon wafer. The following illustrates a method forimproving the carbon content of a polycrystalline silicon column duringthe growing process of the polycrystalline silicon column, which caneffectively improve the photoelectric conversion efficiency of a solarsilicon wafer. Furthermore, in addition to having a higher carboncontent, the polycrystalline silicon column or polycrystalline siliconwafer manufactured by the embodiments of the disclosure also has thecharacteristics of an average grain size of the silicon grains increasedprogressively along the crystal-growing direction, a smaller averagedefect area ratio, and the like.

Herein, the term “polycrystalline silicon column” may be apolycrystalline silicon ingot, a polycrystalline silicon brick, or anyother polycrystalline silicon column having any cross-section shape orsize. For example, the cross-section shape of the polycrystallinesilicon column may be a polygon, such as a square, circular, or othergeometrical shapes. Herein, the term “polycrystalline silicon ingot”refers to a polycrystalline silicon column formed by cooling along acrystal-growing direction after the silicon is melted in a mold. In someembodiments, the cross-section shape of the polycrystalline siliconingot in a direction perpendicular to the crystal-growing direction is asquare, wherein the cross-section size may be for example 690 mm*690 mm,840 mm*840 mm, 1000 mm*1000 mm, or other suitable sizes, and the heightof the cross section may be for example but not limited to 300 mm. Theterm “polycrystalline silicon brick” refers to a polycrystalline siliconcolumn formed by cutting a polycrystalline silicon ingot along acrystal-growing direction. In some embodiments, the cross-section shapeof the polycrystalline silicon brick in a direction perpendicular to thecrystal-growing direction is a square, wherein the cross-section sizemay be for example 156 mm*156 mm or other suitable sizes, and the heightof the cross section may be for example but not limited to 300 mm.Herein, the term “polycrystalline silicon wafer” refers to apolycrystalline silicon wafer formed by cutting a polycrystallinesilicon ingot or polycrystalline silicon brick along a directionperpendicular to the crystal-growing direction. In some embodiments, theshape and size of the polycrystalline silicon wafer is the same as thecross-section shape and size of the polycrystalline silicon brick in adirection perpendicular to the crystal-growing direction, and the widthof the polycrystalline silicon wafer is for example but not limited tobetween 0.1 mm and 3.0 mm.

A reference is made to FIG. 1. FIG. 1 illustrates a DSS (directionalsolidification system) crystal-growing furnace used by a manufacturingmethod according to an embodiment of the disclosure. A DSScrystal-growing furnace 1 includes a furnace body 10, a heat insulationcage 12 consisting of an upper heat-insulation cover 122 and a lowerheat-insulation plate 124, a directional solidification block 18disposed in the heat insulation cage 12, at least one supporting column19 used for supporting the directional solidification block 18, a boxbody 16 disposed on the directional solidification block 18, a mold 4disposed in the box body 16, a heater 13 disposed above the mold 4, anda inert-gas tube 11 passing through the furnace body 10 and the heatinsulation cage 12. In this embodiment, the mold 4 may be a quartzcrucible or a mold made of other heat-resistant materials; thedirectional solidification block 18 may be made of graphite or otherheat-resistant materials; the box body 16 includes a base 162 and anupper cover plate 164, and may be made of graphite or otherheat-resistant materials; and the inert-gas tube 11 is used forintroducing inert gases such as argon into the heat insulation cage 12.In this embodiment, the melting point of the box body 16 is higher thanthat of the mold 4, such that the deformation of itself can be avoidedand thus the deformation of the mold 4 under heat can be prevented, andmeanwhile the contaminants in the DSS crystal-growing furnace 1 can beisolated, such as the dust of oxide, carbide and carbon elementgenerated under a high temperature.

A reference is made to FIG. 2 as well as FIG. 1. FIG. 2 illustrates amethod for manufacturing a polycrystalline silicon ingot according to anembodiment of the disclosure. The method for manufacturing apolycrystalline silicon ingot according to the embodiment includes thefollowing steps. First, a nucleation promotion layer 2 is placed ontothe bottom portion of the mold 4, and then the silicon raw material isplaced into the mold 4. Then, the mold 4 filled with the silicon rawmaterial is placed into the DSS crystal-growing furnace 1 as shown inFIG. 1, wherein the mold 4 is placed in the base 162 of the box body 16,but the upper cover plate 164 of the box body 16 is removed deliberatelyto expose the mold 4 in the DSS crystal-growing furnace 1. Under heatingby the DSS crystal-growing furnace 1, the silicon raw material iscompletely melted into a silicon melt 8, and the nucleation promotionlayer 2 is partially melted, while other parts of the nucleationpromotion layer 2 are not melted. Thereafter, the mold 4 is cooledthrough a directional solidification process, such that a plurality ofpolycrystalline silicon grains gradually grow along a crystal-growingdirection (V) to form a polycrystalline silicon ingot with a highercarbon content. In this embodiment, the silicon raw material is meltedinto a silicon melt 8 under the situation that the upper cover plate 164of the box body 16 is removed. That is, the polycrystalline silicongrains grow from the silicon raw material under the environment that thesilicon raw material is exposed in the DSS crystal-growing furnace 1,and since the elemental materials, such as the carbon fiber insulationmaterial and the heat conduction material made from a graphite plate, ofthe DSS crystal-growing furnace 1 all includes carbon, the carbide andcarbon elements generated under the high temperature conditions usedreadily enter into the silicon melt 8, such that the manufacturedpolycrystalline silicon ingot has a higher carbon content.

In an embodiment of the disclosure, the operation of the DSScrystal-growing furnace 1 is as follows, but not limited to this. (1)The temperature rise from a heating portion to a melting portion isgreater than 1414° C., such that the melting of the silicon raw materialis started. (2) When the temperature of the silicon melt is increased to1500-1570° C., the heat insulation cage 12 is opened to 1-7 cm, suchthat the temperature of the directional solidification block 18 is about1350-1400° C., and the remaining height of the crushed bottom material(nucleation promotion layer 2) is controlled to be 50-70 mm; when thetemperature of the silicon melt is decreased to 1450-1500° C., the heatinsulation cage 12 is opened to 1-8 cm, such that the temperature of thedirectional solidification block 18 is not greater than 1330-1350° C.,and the remaining height of the crushed bottom material (nucleationpromotion layer 2) is controlled to be 30-50 mm; and when thetemperature of the silicon melt is decreased to 1390-1450° C., the heatinsulation cage 12 is opened to 1-8 cm, such that the temperature of thedirectional solidification block 18 is not greater than 1320-1340° C.,and the remaining height of the crushed bottom material (nucleationpromotion layer 2) is controlled to be 15-30 mm, and then the processenters the crystal-growing portion again. (3) The initial temperature ofthe crystal-growing portion is set as 1385-1430° C., the finaltemperature is set as 1385-1400° C., and the heat insulation cage 12 isopened from the initial 1-6 cm to the final 15-30 cm, so as to completethe crystal growing. (4) After the crystal growing is completed, theannealing and cooling processes are completed sequentially.

In one or more embodiments, the nucleation promotion layer 2 consists ofmultiple crystalline particles with irregular and non-uniform shapes,and the grain size of each crystalline particle is less than about 50mm, and preferably less than about 10 mm. For example, the crystallineparticles may be crushed pieces of polycrystalline or monocrystallinematerials. In one or more embodiments, the crystalline particles may bepolycrystalline silicon particles, monocrystalline silicon particles,monocrystalline silicon carbide particles, or other crystallineparticles which are formed by a material with a melting point greaterthan about 1400° C., and promote nucleation. In another embodiment ofthe disclosure, the nucleation promotion layer is a plate body formed bya material with a melting point greater than about 1400° C., and thesurface of the plate body in contact with the melted silicon soup has aroughness in a range from 300 μm to 1000 μm, so as to provide multiplenucleation points.

A reference is made to FIG. 3. FIG. 3 illustrates a method formanufacturing a polycrystalline silicon ingot according to a controlexample of the disclosure. The method for manufacturing thepolycrystalline silicon ingot of the control example uses a wholemelting process, which doesn't use the nucleation promotion layer, andthe crystal grows after the silicon raw materials are completely melted.The manufacturing method of the control example includes the followingsteps. The silicon raw material is put into the mold 4; then the mold 4filled with the silicon raw material is put into the DSS crystal-growingfurnace 1 as shown in FIG. 1, wherein the mold 4 is placed in the boxbody 16, and the box body 16 is covered by the upper cover plate 164.First, the silicon raw material is completely melted into the siliconmelt 8 in the DSS crystal-growing furnace 1. Thereafter, the mold 4 iscooled through a directional solidification process, such that aplurality of polycrystalline silicon grains gradually grow along acrystal-growing direction (V) to form a polycrystalline silicon ingot.As compared with the embodiments of the disclosure in which during thecrystal-growing process, the upper cover plate 164 of the box body 16 isremoved deliberately such that parts of the carbide and carbon elementsgenerated under the high temperature are added into the silicon melt 8;in the control example of the disclosure, during the crystal-growingprocess, the upper cover plate 164 of the box body 16 is not removed,such that no carbon element is added into the silicon melt 8. It can beseen from the above that the polycrystalline silicon column formed byusing the manufacturing method of the present disclosure has a highercarbon content.

In an embodiment of the disclosure, a carrier lifetime tester (u-PCD;Microwave Lifetime Tester) may be used to measure a relationship curveof the minority carrier lifetime of the polycrystalline silicon columnversus the crystal-growing direction (V). The carrier lifetime testeruses a measuring head to irradiate a laser pulse onto a region of thepolycrystalline silicon column with a higher carbon content, such thatelectrons and electron holes are excited, then a microwave is used toirradiate the region already excited by the laser pulse, and then thetime of the carrier separating from and combining with the siliconcrystal is measured; and thereafter, the measuring head is moved alongthe crystal-growing direction (V) to perform the measurement, such thata relationship curve of the minority carrier lifetime versus thecrystal-growing direction (V) is formed. After the relationship curve ofthe minority carrier lifetime (life time) of various portions of thepolycrystalline silicon column versus the crystal-growing direction (V)is obtained, the minority carrier lifetime can be used as a standard fordefining an available section and an unavailable section of thepolycrystalline silicon column. In the disclosure, the carrier lifetimetester can be used for measuring the minority carrier lifetime of thepolycrystalline silicon ingot or the polycrystalline silicon brick.

A reference is made to FIG. 4. FIG. 4 illustrates a relationship curveof the minority carrier lifetime of the polycrystalline silicon columnaccording to an embodiment of the disclosure versus the crystal-growingdirection, wherein the longitudinal axis is the minority carrierlifetime, and the horizontal axis is the height ratio of the availablesection of the polycrystalline silicon column. In one or moreembodiments, a section with a minority carrier lifetime greater than orequal to a specific value is defined as an available section, while asection with a minority carrier lifetime less than the specific value isdefined as an unavailable section which can be cut and removed. Forexample, in one or more embodiments, a section of the polycrystallinesilicon column with a minority carrier lifetime greater than or equal to2.0×10⁻⁶ seconds is defined as an available section, and a section witha minority carrier lifetime less than 2.0×10⁻⁶ seconds is defined as anunavailable section which can be cut off and removed. As shown in FIG.4, in general, the sections located at the bottom end and the top end ofthe polycrystalline silicon column are sections with low carrierlifetimes, i.e., unavailable sections to be cut off and removed, and thesections remaining after the unavailable sections are cut off andremoved are available sections. In an embodiment, along thecrystal-growing direction (V) the available section may further includea bottom section, a middle section and a top section, wherein the ratioof the bottom section, the middle section and the top section is definedaccording to the resistivity, the average defect area ratio, the oxygencontent, the average grain size and other characteristics. For example,in one or more embodiments, an available section of the polycrystallinesilicon column in which the average grain size of the polycrystallinesilicon column in the crystal-growing direction and the resistivity ofthe polycrystalline silicon column have the opposite variation in theirtrends, the resistivity is greater than or equal to 1.55 Ω-cm, or theaverage grain size is less than or equal to 1.0 cm, or the oxygencontent is greater than or equal to 5.5 ppma is considered as the bottomsection. In one or more embodiments, an available section of thepolycrystalline silicon column in which the average grain size of thepolycrystalline silicon column in the crystal-growing direction and theoxygen content have the opposite variation in their trends, theresistivity is greater than or equal to 1.55 Ω-cm, or the average grainsize less than or equal to 1.0 cm, or the oxygen content is greater thanor equal to 5.5 ppma is considered as the bottom section. In one or moreembodiments, an available section of the polycrystalline silicon columnin which the average grain size of the polycrystalline silicon column inthe crystal-growing direction and the defect area ratio have the samevariation in their trend, the resistivity is greater than or equal to1.55 f-cm, or the average grain size less than or equal to 1.0 cm, orthe oxygen content is greater than or equal to 5.5 ppma is considered asthe bottom section.

In an embodiment, the crystal orientation distribution of the silicongrains in the polycrystalline silicon column may be analyzed throughelectron back-scattered diffraction (EBSD). A reference is made toTable 1. Table 1 illustrates an analysis result of the crystalorientation distribution of the silicon grains in the polycrystallinesilicon column according to an embodiment of the disclosure andaccording to a control example. It can be seen from the upper halfportion of table 1 that, in addition to the crystal orientations {111},{112}, {113}, {315} and {115}, the polycrystalline silicon column of theembodiment also include crystal orientations {100}, {313} and {101}. Inan embodiment, using the bottom end of the available section of thepolycrystalline silicon column as a baseline, the crystal orientationdistribution measured at the position with a height ratio of about 1% isconsidered as the crystal orientation distribution of the bottomsection; the crystal orientation distribution measured at the positionwith a height ratio of about 50% is considered as the crystalorientation distribution of the middle section; and the crystalorientation distribution measured at the position with a height ratio ofabout 100% is considered as the crystal orientation distribution of thetop section.

The volume percent sum of the silicon grains having the crystalorientations {112}, {113} and {115} in the bottom section of thepolycrystalline silicon column according to one or more embodimentsaccounts for greater than 45% of the overall silicon grains withdifferent crystal orientations in the polycrystalline silicon column;the volume percent sum of the silicon grains having the crystalorientation {112} in the bottom section accounts for between 25% and 30%of the overall silicon grains with different crystal orientations in thepolycrystalline silicon column; and the volume percent of the silicongrains having the crystal orientation {112} in the bottom section isgreater than the volume percent of the silicon grains having the crystalorientation {113} or {115} in the bottom section. For example, it can beseen from Table 1 that the volume percent sum of the silicon grainshaving the crystal orientations {112}, {113} and {115} in the bottomsection of the polycrystalline silicon column according to one or moreembodiments accounts for about 50.7% of the overall silicon grains withdifferent crystal orientations in the polycrystalline silicon column;the volume percent sum of the silicon grains having the crystalorientation {112} in the bottom section accounts for about 26.2% of theoverall silicon grains with different crystal orientations in thepolycrystalline silicon column; and the volume percent of the silicongrains having the crystal orientation {112} in the bottom section isgreater than the volume percent of the silicon grains having the crystalorientation {113} or {115} in the bottom section. On the other hand, thevolume percent sum of the silicon grains having the crystal orientations{112}, {113} and {115} in the bottom section of the polycrystallinesilicon column according to the control example only accounts for 44.8%of the overall silicon grains with different crystal orientations in thepolycrystalline silicon column. That is, the volume percent of the threecrystal orientations {112}, {113} and {115} is less than 45%, whereinthe volume percent of the silicon grains having the crystal orientation{112} in the bottom section is less than the volume percent of thesilicon grains having the crystal orientation {113} or {115} in thebottom section, and the volume percent of the silicon grains having thecrystal orientation {112} in the bottom section only 5.8%. That is, thevolume percent of the crystal orientation {112} is less than the rangeof 25%-30%.

TABLE 1 {100} {101} {111} {112} {113} {115} {313} {315} Embodiment ofThe Application The 2.1 2.6 16.1 26.2 11.0 13.5 3.8 25.1 bottom positionThe 1.8 2.6 21.1 28.3 8.3 18.7 4.4 15.8 middle position The 0.4 0.4 17.519.7 11.5 29.6 3.7 17.5 top position Control Example The 0.3 8.3 11.35.8 30.2 8.8 7.9 23.3 bottom position The 0.8 9.9 20.3 16.3 16.8 8.613.7 16.1 middle position The 1.1 8.3 17.7 25.3 16.6 9.7 7.6 13.7 topposition

A reference is made to FIGS. 5 and 6. FIG. 5 is a relationship graph ofpolycrystalline silicon columns according to an embodiment of thedisclosure, between the carbon content in the crystal-growing directionand the height ratio of the available section of the polycrystallinesilicon columns; and FIG. 6 is a relationship graph of polycrystallinesilicon columns according to a control example, between the carboncontent in the crystal-growing direction and the height ratio of theavailable section of the polycrystalline silicon columns, wherein thelongitudinal axis is the carbon content, and the horizontal axis is theheight ratio of the available section of the polycrystalline siliconcolumns in the crystal-growing direction. As shown in FIGS. 5 and 6,according to the measuring results of multiple groups of polycrystallinesilicon column samples, the carbon content distribution at differentpositions of the polycrystalline silicon column according to theembodiment in the crystal-growing direction (V) is relatively even,while the carbon content distribution at different positions of thepolycrystalline silicon column according to the control example in thecrystal-growing direction (V) is relatively uneven and are obviouslypresented as being increased progressively. Furthermore, as comparedwith the control example, the overall carbon content of thepolycrystalline silicon column of the embodiments according to thepresent disclosure is obviously higher, especially for the carboncontent in the bottom section.

A reference is made to FIG. 7. FIG. 7 is a distribution diagram of thecarbon content in the bottom section of the polycrystalline siliconcolumn according to an embodiment of the disclosure. As shown in FIG. 7,in this embodiment, more than 80% of the polycrystalline silicon columnin the bottom section has a carbon content greater than or equal to 4ppma, and for example, about 88% of the polycrystalline silicon columnin the bottom section has a carbon content greater than or equal to 4ppma; more than 60% of the polycrystalline silicon column in the bottomsection has a carbon content greater than or equal to 5 ppma, and forexample, about 68% of the polycrystalline silicon column in the bottomsection has a carbon content greater than or equal to 5 ppma; and morethan 25% of the polycrystalline silicon column in the bottom section hasa carbon content greater than or equal to 6 ppma, and for example, about29% of the polycrystalline silicon column in the bottom section has acarbon content greater than or equal to 6 ppma. Accordingly, more than80% of the polycrystalline silicon wafer manufactured by cutting thebottom section of the polycrystalline silicon column according to thisembodiment has a carbon content greater than 4 ppma; more than 60% ofthe polycrystalline silicon wafer has a carbon content greater than 5ppma; and more than 25% of the polycrystalline silicon wafer has acarbon content greater than 6 ppma.

A reference is made to FIG. 8. FIG. 8 is a distribution diagram of thecarbon content of the bottom section of the polycrystalline siliconcolumn according to a control example. As shown in FIG. 8, in thecontrol example, only more than 4% of the polycrystalline silicon columnin the bottom section has a carbon content greater than or equal to 4ppma. That is, most of the polycrystalline silicon column according tothe control example in the bottom section has a carbon content less than4 ppma, which is obviously different from the carbon contentdistribution in the bottom section of the polycrystalline silicon columnof this embodiment.

The aforementioned carbon contents of the polycrystalline siliconcolumns according to the embodiments of the disclosure and according tothe control example are measured by using a Fourier transform infraredspectroscopy (FTIR) measuring instrument, with reference to the SEMI MF1391-0704 standard measurement specification. A reference is made toFIG. 9. FIG. 9 illustrates a schematic diagram of a location formeasuring the carbon content of the polycrystalline silicon column ofthe embodiment. The particular measuring method of the carbon content ofthe polycrystalline silicon column of this embodiment is as follows.First, the polycrystalline silicon column is cut into a plurality oftest specimens. Then, the carbon contents at nine different positions ofa test specimen is measured using the FTIR measuring instrument.Finally, an average value of the respective carbon contents of the ninepositions on the test specimen as measured in a single test iscalculated, and an overall average value obtained after the test isrepeated for five times is regarded as the carbon content of this testspecimen. As shown in FIG. 9, the test specimen of the embodiment is asquare test specimen with a size of 156 mm*156 mm and a width between0.1 mm and 3 mm, such as 0.2 mm or 2 mm. The position 1 on the testspecimen is the cross-point position of two diagonal lines. Thepositions 2, 5, 6 and 9 are symmetric about the symmetric center,position 1, and are respectively located on the diagonal lines, beingaway from the respective adjacent corners with a distance of about 10mm. The positions 3, 4, 7 and 8 are symmetric about the symmetriccenter, position 1, and are respectively located on the diagonal lines,being away from the position 1 with a distance of about 50.8 mm.Additionally, the relationship of the carbon content of thepolycrystalline silicon column in the bottom section as mentioned inFIGS. 7 and 8 refers to a relationship which is obtained by cutting thebottom section into multiple pieces of test specimens, measuring thecarbon contents of respective test specimens in the aforementioned way,and then carrying out a statistics of the ratio of the number of testspecimens with different carbon contents to the number of overall testspecimens. For example, if the bottom section of the polycrystallinesilicon column is cut into 100 pieces of test specimens, then after thecarbon content of each of the 100 pieces of test specimens is measuredin the aforementioned way, the test specimens are divided into severalgroups based on the carbon contents (for example, the carbon content ofthe first group is greater than or equal to 0 ppma and is less than 1ppma; the carbon content of the second group is greater than or equal to1 ppma and is less than 2 ppma, and so on), and finally statistical dataof the carbon content in the bottom section of the polycrystallinesilicon column can be obtained. For example, more than 80% of thepolycrystalline silicon column according to this embodiment in thebottom section has a carbon content greater than or equal to 4 ppma.That is, at least 80 of the 100 pieces of test specimens cut from thebottom section of the same polycrystalline silicon column have a carboncontent greater than or equal to 4 ppma.

It can be seen from the above that, carbon is deliberately added duringthe crystal-growing process of the manufacturing method of the presentdisclosure, such that the formed polycrystalline silicon ingot may havea higher carbon content, especially in the bottom section, and thus thepolycrystalline silicon brick or polycrystalline silicon wafer formed bycutting the polycrystalline silicon ingot with a higher carbon contenthas a lower defect area ratio and therefore a higher photoelectricconversion efficiency.

A reference is made to FIG. 10. FIG. 10 is a relationship graph betweenthe average grain sizes of the silicon grains of the polycrystallinesilicon columns according to an embodiment of the disclosure andaccording to a control example and the available-section height ratiosof the polycrystalline silicon columns, wherein the longitudinal axis isthe average grain size, and the horizontal axis is the height ratio ofthe available section of the polycrystalline silicon column in thecrystal-growing direction. As shown in FIG. 10, according to themeasuring results of multiple groups of polycrystalline silicon columnsamples, for the grain size of the silicon grains in the polycrystallinesilicon column (including the polycrystalline silicon ingot or thepolycrystalline silicon brick) manufactured by the method of thedisclosure, the average grain size in the available section of thepolycrystalline silicon column is increased progressively along thecrystal-growing direction (V). Furthermore, it can be seen from FIG. 10that the average grain size of silicon grains at each position in theavailable section of the polycrystalline silicon column is less than orequal to 1.26 cm, the overall average grain size of the silicon grainsin the available section of the polycrystalline silicon column is lessthan or equal to 1.1 cm, and specifically the average grain size of thesilicon grains in the bottom section is less than or equal to 1.0 cm. Onthe other hand, the average grain size of the silicon grains in thepolycrystalline silicon column according to the control example isdecreased progressively along the crystal-growing direction (V).Furthermore, the overall average grain size of the silicon grainslocated in the available section of the polycrystalline silicon columnaccording to the control example is greater than 1.26 cm, andspecifically the average grain size in the bottom section is obviouslygreater than 1.4 cm.

The aforementioned average grain sizes of the embodiment of thedisclosure and of the control example are measured according to the ASTME112-10 standard measurement specification. For example, thepolycrystalline silicon column sample is cut along the crystal-growingdirection (V) into multiple test specimens, each piece of the testspecimens are scanned to form an image thereof, then the number ofsilicon grains are observed along the diagonal line, and the averagegrain size is calculated according to the diagonal line length of thetest specimen and the number of silicon grains.

A reference is made to FIG. 1I. FIG. 11 is a distribution diagram of thepolycrystalline silicon ingot according to an embodiment of thedisclosure versus the ratio of an average grain size in thecrystal-growing direction to the radial length of the crystalline ingot,wherein the longitudinal axis is the ratio of the average grain size tothe radial length of the cross section of the polycrystalline siliconingot in a direction perpendicular to the crystal-growing direction, andthe horizontal axis is the height ratio of the available section of thepolycrystalline silicon ingot in the crystal-growing direction.Additionally, the radial length of the crystalline ingot of a sample 1is between 675 mm and 690 mm, wherein a section with the ratio of theaverage grain size to the radial length of the crystalline ingot lessthan 0.0135 is defined as the bottom section; the radial length of thecrystalline ingot of a sample 2 is between 820 mm and 855 mm, wherein asection with the ratio of the average grain size to the radial length ofthe crystalline ingot less than 0.0110 is defined as the bottom section;the radial length of the crystalline ingot of a sample 3 is between 975mm and 1015 mm, wherein a section with the ratio of the average grainsize to the radial length of the crystalline ingot less than 0.0093 isdefined as the bottom section; and the radial length of the crystallineingot of a sample 4 is between 1320 mm and 1330 mm, wherein a sectionwith the ratio of the average grain size to the radial length of thecrystalline ingot less than 0.0071 is defined as the bottom section. Asshown in FIG. 11, the ratio of the average grain size in the bottomsection of the polycrystalline silicon ingot to the radial length of thecrystalline ingot is less than or equal to 0.01. In this embodiment,since the polycrystalline silicon ingot is formed by growing in a mold(e.g., a crucible), the ratio of the average grain size of the silicongrains in the bottom section of the polycrystalline silicon ingot to thesize of the mold also comply with the aforementioned performance.

A reference is made to FIG. 12. FIG. 12 is a distribution diagram of thepolycrystalline silicon ingot according to a control example versus theratio of an average grain size in the crystal-growing direction to theradial length of the crystalline ingot, wherein the longitudinal axis isthe ratio of the average grain size to the radial length of the crosssection of the polycrystalline silicon ingot in a directionperpendicular to the crystal-growing direction, and the horizontal axisis the height ratio of the available section of the polycrystallinesilicon ingot in the crystal-growing direction. Additionally, the radiallength of the crystalline ingot of a sample 1′ is between 675 mm and 690mm; the radial length of the crystalline ingot of a sample 2′ is between820 mm and 855 mm; the radial length of the crystalline ingot of asample 3′ is between 975 mm and 1015 mm; and the radial length of thecrystalline ingot of a sample 4′ is between 1320 mm and 1330 mm. Asshown in FIG. 12, in the control example, the ratio of the overallaverage grain size in the available section of the polycrystallinesilicon ingot to the radial length of the crystalline ingot is greaterthan 0.01.

A reference is made to FIG. 13. FIG. 13 is a distribution diagram of apolycrystalline silicon brick according to an embodiment of thedisclosure versus the ratio of an average grain size in thecrystal-growing direction to the radial length of the polycrystallinesilicon brick, wherein the longitudinal axis is the ratio of the averagegrain size to the radial length of the cross section of thepolycrystalline silicon brick in a direction perpendicular to thecrystal-growing direction, and the horizontal axis is the height ratioof the available section of the polycrystalline silicon brick in thecrystal-growing direction. As shown in FIG. 13, the average ratio of theoverall average grain size in the available section of thepolycrystalline silicon brick according to this embodiment to the radiallength of the crystalline silicon brick is less than or equal to 0.08,and specifically the average ratio of the grain size in the bottomsection to the radial length of the polycrystalline silicon brick isless than or equal to 0.061. The polycrystalline silicon brick of thisembodiment may be cut along the crystal-growing direction (V) to form apolycrystalline silicon wafer, and the width of the polycrystallinesilicon wafer is substantially equal to the radial length of the crosssection of the polycrystalline silicon brick. In other words, in thepolycrystalline silicon wafer formed by cutting the bottom section ofthe polycrystalline silicon brick of this embodiment, the ratio of theaverage grain size of the silicon grains to the radial length of thecross section of the polycrystalline silicon wafer also performed asbefore. On the other hand, in the control example, the average ratio ofthe overall average grain size in the available section of thepolycrystalline silicon brick to the radial length of thepolycrystalline silicon brick is greater than 0.08, which is greaterthan that of the embodiment.

A reference is made to FIG. 14. FIG. 14 is a relationship diagrambetween the resistivity of a polycrystalline silicon column according toan embodiment of the disclosure and the height ratio of the availablesection of the polycrystalline silicon column, wherein the longitudinalaxis is the resistivity of the polycrystalline silicon column, and thehorizontal axis is the height ratio of the available section of thepolycrystalline silicon column in the crystal-growing direction. Asshown in FIG. 14, according to the measuring results of multiple groupsof polycrystalline silicon column samples, for the resistivity of thepolycrystalline silicon column (including the polycrystalline siliconingot or the polycrystalline silicon brick) manufactured by the methodof the disclosure, the resistivity of a sample having either a largestresistivity value or a smallest resistivity value is decreasedprogressively along the crystal-growing direction (V), and thus theaverage resistivity value calculated from the multiple groups of samplesis also decreased progressively along the crystal-growing direction (V).In other words, with reference to FIGS. 10 and 14, it can be observedthat in the crystal-growing direction (V) the average grain size of thesilicon grains in the polycrystalline silicon column manufactured by themethod of the disclosure and the resistivity of the polycrystallinesilicon column have the opposite variation in their trends. Furthermore,it can be seen from FIG. 14 that the resistivity in the bottom sectionof the polycrystalline silicon column is greater than or equal to 1.55Ω-cm, for example between 1.55 Ω-cm and 1.9 Ω-cm, and thus theresistivity of the polycrystalline silicon wafer formed by cutting thebottom section of the polycrystalline silicon column of this embodimentis also greater than or equal to 1.55 Ω-cm.

In this embodiment, the measurement of resistivity is performed usingthe following method. A side face of the polycrystalline silicon columnis tested using a non-contact resistivity meter, and the average valueof values measured at four sides of the polycrystalline silicon columnat each height is considered as the resistivity of this height; or thewafer cut from the polycrystalline silicon column is detected using thenon-contact resistivity meter, such that the resistivity of each waferis obtained, and the resistivity variation at respective heights can beknown by arranging the wafers along the crystal-growing direction. Thenon-contact resistivity measuring method is performed as follows. An ACcurrent with a fixed frequency is introduced onto a transmitting coil,and then when the magnetic field generated by the coil approaches theobject to be measured, an eddy current occurs in the object to bemeasured. The strength of the eddy current is inversely proportional tothe resistivity, and thus the resistivity of the object to be measuredcan be obtained.

A reference is made to FIG. 15. FIG. 15 is a relationship graph betweenthe oxygen content of a polycrystalline silicon column according to anembodiment of the disclosure and the height ratio of the availablesection of the polycrystalline silicon column, wherein the longitudinalaxis is the oxygen content, and the horizontal axis is the height ratioof the available section of the polycrystalline silicon column in thecrystal-growing direction. The measuring and sampling manners of theoxygen content of the polycrystalline silicon column according to theembodiment are similar to that of the carbon content of thepolycrystalline silicon column according to the aforementionedembodiment. That is, the polycrystalline silicon column is cut into aplurality of test specimens, the oxygen contents at different positionson the test specimen are measured by using the FTIR measuring instrumentwith reference to the ASTM MF1188-1105 standard measurementspecification, and then an average value of the oxygen contents is takenas the oxygen content of the test specimen. The oxygen contents of alltest specimens represent the oxygen contents of the polycrystallinesilicon column at different positions in the crystal-growing direction.As shown in FIG. 15, according to the measuring results of multiplegroups of polycrystalline silicon column samples, the oxygen contents ofthe polycrystalline silicon columns (including the polycrystallinesilicon ingot or the polycrystalline silicon brick) manufactured by themethod of the disclosure are all decreased progressively along thecrystal-growing direction (V). In other words, with reference to FIGS.10 and 15, it can be observed that in the crystal-growing direction (V)the average grain size of the silicon grains in the polycrystallinesilicon column manufactured by the method of the disclosure and theoxygen content of the polycrystalline silicon column have the oppositevariation in their trends. Furthermore, it can be seen from FIG. 15that, the oxygen content in the bottom section of the available sectionof the polycrystalline silicon column is greater than or equal to 5.5ppma.

A reference is made to FIG. 16. FIG. 16 is a relationship graph betweenthe defect area ratio of the polycrystalline silicon column according toan embodiment of the disclosure and the height ratio of the availablesection of the polycrystalline silicon column, wherein the longitudinalaxis is the defect area ratio, and the horizontal axis is the heightratio of the available section of the polycrystalline silicon column. Inthis embodiment, the detection manner of the defect area ratio isperformed by detecting with a photoluminescence (PL) meter, wherein alight with energy higher than the semiconductor energy gap is irradiatedonto the polycrystalline silicon to generate a fluorescent light emitteddue to carrier transition and complex behaviors, then a defect positionis determined by a measuring system according to a fluorescence spectra,and the defect area ratio is thus calculated. First, with reference toFIGS. 10 and 16, it can be seen that in the crystal-growing direction(V), the average grain size of the silicon grains in the polycrystallinesilicon column manufactured by the method of the disclosure and thedefect area ratio of the polycrystalline silicon column have the samevariation in their trends. Furthermore, as shown in FIG. 16, the defectarea ratios at respective positions in the available section of thepolycrystalline silicon column (including the polycrystalline siliconingot or the polycrystalline silicon brick) manufactured by the methodof the disclosure are all less than 3.5%, and the overall average defectarea ratio in the available section of the polycrystalline siliconcolumn is less than or equal to 2.5%, and specifically the averagedefect area ratio in the bottom section is less than or equal to 1.5%.Therefore, a wafer formed by cutting a polycrystalline silicon columnformed according to the present disclosure has a higher photoelectricconversion efficiency. As compared, the overall average defect arearatio in the available section of the polycrystalline silicon columnmanufactured by the whole melting process of the control example isgreater than 4%, and thus a wafer cut from the polycrystalline siliconcolumn has a lower photoelectric conversion efficiency.

In the manufacturing method of the disclosure, during thecrystal-growing process, the silicon melt is exposed to acarbon-containing environment, and thus the formed polycrystallinesilicon column has a higher carbon content, and especially the bottomsection has a higher carbon content. As such, the polycrystallinesilicon wafer formed by cutting the polycrystalline silicon column witha higher carbon content also has a higher carbon content and a lowerdefect area ratio, and accordingly a higher photoelectric conversionefficiency. Furthermore, in addition to having a higher carbon content,the polycrystalline silicon column or polycrystalline silicon wafermanufactured by the method of the disclosure also has thecharacteristics of an average grain size of the silicon grains thatincrease progressively along the crystal-growing direction, a smalleraverage defect area ratio, a smaller average grain size of the silicongrains, and the like.

In the prior art, those of ordinary skills believe that if thepolycrystalline silicon ingot has a lower carbon content, then thequality of the polycrystalline silicon ingot is better; and in contrast,if the carbon content is too high, a problem of silicon carbideprecipitates occurs, which causes a decreased yield of thepolycrystalline silicon wafer made from the polycrystalline siliconingot, an even a increase of current leakage, thereby reducing thephotoelectric conversion efficiency. The present disclosure steps outfrom the narrow view of the prior art, which adds carbon into thecrystal-growing process deliberately so as to manufacture apolycrystalline silicon ingot with a higher carbon content. Specificallythe polycrystalline silicon ingot has a higher carbon content in thebottom section, and thus the polycrystalline silicon brick orpolycrystalline silicon wafer formed by cutting the polycrystallinesilicon ingot with a higher carbon content also has the characteristicsof a higher carbon content and a lower defect area ratio, andaccordingly a higher photoelectric conversion efficiency.

The features of some implementations are described in brief, and thusthose skilled in the art can understand aspects of the disclosurebetter. It should be understood by those skilled in the art that, thedisclosure of the application can be readily used as a basis to designor modify other processes and structures, thereby achieving the samepurposes and/or same advantages as the implementation of theapplication. It should be understood by those skilled in the art that,such an equivalent architecture does not depart from the spirit andscope of the disclosure of the application, and various changes,substitutions and replacements can be made by those skilled in the artwithout departing from the spirit and scope of the disclosure of theapplication.

What is claimed:
 1. A polycrystalline silicon wafer, comprising: aplurality of silicon grains, wherein the carbon content of thepolycrystalline silicon wafer is greater than 4 ppma, the resistivity ofthe polycrystalline silicon wafer is greater than or equal to 1.55 Ω-cm,and an average defect area ratio of the polycrystalline silicon wafer isless than or equal to 1.5%.
 2. The polycrystalline silicon wafer ofclaim 1, wherein the silicon grains comprise at least three crystalorientations, the at least three crystal orientations comprise {112},{113} and {115}; and wherein the volume percent of the silicon grainshaving the crystal orientations {112}, {113} and {115} is greater than45%.
 3. The polycrystalline silicon wafer of claim 2, wherein the volumepercent of the silicon grains having the crystal orientation {112} isbetween 25% and 30%.
 4. The polycrystalline silicon wafer of claim 1,wherein the polycrystalline silicon wafer has a width, and the ratio ofthe average grain size of the silicon grains to the width of thepolycrystalline silicon wafer is less than or equal to 0.061.
 5. Thepolycrystalline silicon wafer of claim 1, wherein the average grain sizeof the silicon grains is less than or equal to 1.0 cm.
 6. Thepolycrystalline silicon wafer of claim 1, wherein the oxygen content ofthe polycrystalline silicon wafer is greater than or equal to 5.5 ppma.7. The polycrystalline silicon wafer of claim 1, wherein the carboncontent of the polycrystalline silicon wafer is greater than or equal to5 ppma.